1. Field of the Invention
The present invention relates generally to an image scanning apparatus using laser light, and in particular, to an image scanning apparatus utilizing a line scan or spot scan method.
2. Description of the Related Art
In an image scanning apparatus for embodying an image on a screen, lights emitted from light sources for generating visible lights having wavelength bandwidths different from each other are irradiated in a line pattern to the screen through a scanning mirror. The scanning mirror can employ a rotational polygon mirror, a galvanometer mirror, and a micro electromechanical system (MEMS) mirror. The scanning mirror performs a plurality of line scans or spot scans repeatedly within a predetermined viewing angle range, thereby embodying the image on the screen. However, there can be a drawback in that an optical device, such as a general scanning mirror, is out of a viewing angle range due to external environmental causes such as temperature change and aging. To address this, a projection image apparatus typically includes various monitoring units for monitoring the viewing angle range of the scanning mirror.
A servo-loop monitoring unit using a position sensor and a monitoring unit using a galvanometer are available as monitoring units, in which a position signal is detected using varying capacitance depending on the motor rotation in order to control a motor driving signal.
In the servo-loop monitoring unit, after the position signal detected using the position sensor is converted into an electrical signal, the electrical signal is fed back to an actuator, which is a driver of the scanning mirror, thereby controlling and performing the exact scan within a desired viewing angle.
Meanwhile, the position sensor employs an electrostatic combo driver or a piezoelectric device sensor. In the electrostatic combo driver, capacitance variation generated from a combo structure when a MEMS mirror rotates around a hinge is converted into an electrical signal, and the electrical signal is fed back to the scanning mirror, thereby controlling the position. The piezoelectric device sensor employing a piezoelectric device has been made public in Journal of Micro electro mechanical systems, Vol. 11, No. 4, 2002, P.355.
However, there is a drawback in that the position sensor for monitoring the viewing angle range can only be used in a combo driving actuator. Further, if the combo capacitance is decreased due to the increase in the scan angle, a capacitance signal gets smaller, thereby not obtaining an exact measurement value. In other words, the capacitance based monitoring unit has a problem in that the viewing angle range of the scanning mirror is limited.
Furthermore, a monitoring unit using a piezoelectric resistor uses materials formed through a process in which ion impurities are added to a portion of a silicon wafer. As a result, the resistance may be varied depending on temperature. Accordingly, a bridge circuit must be additionally provided to minimize resistance variation affected by the temperature.